var stream = require('stream');
var Readable = stream.Readable;
var c = 'a'.charCodeAt(0);
function MyReadable(){
    Readable.call(this);
};
for(i in Readable.prototype){
    MyReadable.prototype[i] = Readable.prototype[i];
};
MyReadable.prototype.letter = function(){
    this._read=function(){
        if(c<='z'.charCodeAt(0)){
            this.push(String.fromCharCode(c++));
        }else{
            this.push(null);
        }
    }
    this.pipe(process.stdout);
};
module.exports = MyReadable;
